(1) Field of the Invention
The present invention relates to an improved sound rated floor system and a method for constructing same, and more particularly to a novel structure for a sound rated floor comprising an attenuation layer having acoustically semi-transparent first and second facings bonded to a core and a rigid layer positioned above the attenuation layer. Also disclosed is a method for constructing a sound rated floor using such an attenuation layer.
(2) Description of the Prior Art
Sound rated or floating floor systems are known in the prior art for acoustically isolating a room beneath a floor on which impacts may occur, such as pedestrian footfalls, sports activities, dropping of toys, or scraping of furniture being moved.
Impact noise generation can generally be reduced by using thick carpeting, but where concrete, tile, or hardwood finishes are to be used a sound rated floor may be particularly desirable. The transmission of impact noise to the area below can be reduced by resiliently supporting the floor away from the floor substructure, which typically transmits the noise into the area below. If the floor surface receiving the impact is isolated from the substructure, then the impact sound transmission will be greatly reduced. Likewise, if the ceiling below is isolated from the substructure, the impact sound will be restricted from traveling into the area below.
Sound rated floors are typically evaluated by ASTM Standards E90 or #336 and #492 and are rated as to impact insulation class (IIC). The greater the IIC rating, the less impact noise will be transmitted to the area below. Floors may also be rated as to Sound Transmission Class (STC). The greater the STC rating, the less airborne sound will be transmitted to the area below. Sound rated floors typically are specified to have an IIC rating of not less than 50 and an STC rating of not less than 50. Even though an IIC rating of 50 meets many building codes, experience has shown that in luxury condominium applications even floor-ceiling systems having an IIC of 56-57 may not be acceptable because some impact noise is still audible.
In addition to having an adequate STC and IIC rating, an acceptable sound rated floor must also have a relatively low profile. Low profile is important in order to maintain minimum transition height between a finished sound rated floor and adjacent areas, such as carpeted floors, which ordinarily do not need the sound rated construction.
Also, a sound rated floor must exhibit enough vertical stiffness to reduce cracking, creaking, and deflection of the finished covering. At the same time, the sound rated floor must be resilient enough to isolate the impact noise from the area to be protected below.
Two isolation media currently used and also approved by the Ceramic Tile Institute for sound rated tile floors are (i) 0.4 inch Enkasonic matting (nylon and carbon black spinerette extruded 630 g/sq. meter) and (ii) 0.25 inch Dow Ethafoam (polyethylene foam 2.7 pcf). While both of these systems are statically relatively soft and provide some degree of resiliency for impact insulation, the added effect of air stiffness in the 0.25 and 0.40 inch thick media makes the system very stiff dynamically and limits the amount of impact insulation. Because the systems are statically soft, they do not provide a high degree of support for the finished floor, and a relatively thick (7/16 inch) glass mesh mortar board, such as a product called Wonderboard, is used on top of the media to provide rigidity for preventing grout, tiles, and other finished flooring from cracking. Alternatively, a relatively thick (11/4 inch) reinforced mortar bed must be installed on top of the resilient mat.